1. Technical Field of the Invention
The present invention relates to a chamfering method and apparatus for processing the edges of a glass substrate for a hard disk.
2. Prior Art
A hard disk is a storage device of a computer; the surface of a thin doughnut-like circular disk is coated with a magnetic substance in which data are stored. Aluminum has been used conventionally as the material of this circular disk (hereafter referred to as xe2x80x9chard disk substratexe2x80x9d). However, recently, chemically reinforced glass or crystalline glass have been used as the substrate of a hard disk (referred to as xe2x80x9cglass substratexe2x80x9d).
FIGS. 1A and 1B schematically show a glass substrate; FIG. 1A is a general view, and FIG. 1B shows a sectional view of the outer and inner peripheries. For a glass substrate with a nominal size of 2.5 inches, for example, outer and inner diameters are 2.5 and 1 inches (about 63 mm and about 25 mm), respectively, and the thickness is about 1.6 mm. The outer and inner peripheries (also referred to as xe2x80x9cedge portionsxe2x80x9d) are composed of end surfaces (with a width of 0.6 mm) at outer and inner peripheries, and a pair of oblique surfaces sandwiching the peripheries (with an angle of about 45xc2x0).
The aforementioned glass substrate is subjected to high-speed revolutions of several tens thousand revolution per minutes to shorten the access time of the hard disk. Consequently, the entire body thereof must be processed precisely, and a high dynamic balance must be achieved. Both surfaces of the glass substrate are finished to a mirror surface of an Rz of 1 xcexcm or less, so that a magnetic substance can be coated at a high density to maximize memory capacity.
In addition, edges (including end surfaces and oblique surfaces) should be finished to mirror surface quality with such high accuracy and quality as required by both surfaces of the glass substrate. The reason edge portions are finished to mirror surface quality is explained below.
(1) There are microscopic cracks on a rough pear-like surface. As a result, a glass reinforcing treatment may result in unevenness, or cracks may grow due to high-speed revolutions during operation, eventually causing breakage of the substrate.
(2) Contaminants may remain in microscopic recesses of a crack, so cleaning may be incomplete, and it may be a source of contamination in a subsequent process.
Edge portions of the above-mentioned glass substrate were, in the prior art, finished to mirror surface quality first by using a formed plated grindstone,which is highly precise, and then by buffing to mirror surface quality.
However, compared to an aluminum substrate, a glass substrate provides poor machinability, so one problem was that machining efficiency, when using a plated grindstone, was low. More explicitly, although rather coarse grinding particles of #500 (grain diameter of about 30 xcexcm) to #600 (grain diameter of about 25 xcexcm) are used, grinding particles still peel considerably; therefore, the plated grindstone must be replaced frequently, so the continuous processing period with the machine is short and operating ratio is low because the grindstone must be replaced. In addition, since the processed surface is in a pear-like state with a rough surface, buff-polishing must be carried out for a long time (about one hour) as a subsequent process to the machining with the plated grindstone. Consequently, overall productivity is low, which is a practical problem.
The present invention aims to solve these problems. That is, an object of the present invention is to provide a chamfering method and apparatus for the glass substrate of a hard disk, with which edge portions of the substrate can be processed with high accuracy, quality, and efficiency, thereby greatly reducing the need for a subsequent process, such as buff-polishing, or even eliminating it. The present invention provides, as a method of processing end surfaces of outer and inner peripheries of a doughnut-like glass substrate (1) with a circular hole (1a) at the center thereof and chamfering oblique surfaces sandwiching the end surfaces, a glass substrate chamfering method using a metal-bonded outer-surface grindstone (12) for simultaneously processing the end surface and oblique surfaces of the outer periphery, and a metal-bonded inner-surface grindstone (14) for simultaneously processing the end surface and oblique surfaces of the inner periphery, wherein by means of the outer-surface grindstone and the inner-surface grindstone, end surfaces and oblique surfaces of outer and inner peripheries of the glass substrate are ground at the same time, and during a grinding process, the outer-surface grindstone is dressed electrolytically to sharpen the grinding particles, and during a non-processing period to replace the glass substrate, the inner-surface grindstone is dressed electrolytically.
The present invention also provides a chamfering apparatus for processing end surfaces of inner and outer peripheries of the doughnut-like glass substrate (1) having a circular hole (1a) at the center thereof and chamfering oblique surfaces sandwiching the end surfaces, composed of the metal-bonded outer-surface grindstone (12) for processing the end surface and oblique surfaces of the outer periphery, the metal-bonded inner-surface grindstone (14) for simultaneously processing the end surface and oblique surfaces of the inner periphery, the outer-surface electrode (18) for electrolytically dressing the outer-surface grindstone during the grinding process, the inner-surface electrode (20) for electrolytically dressing the inner-surface grindstone during the non-processing period, a grinding liquid feeder (22) for supplying a conductive grinding liquid between the outer-surface grindstone and the outer-surface electrode and between the inner-surface grindstone and the inner-surface electrode, and a voltage application means (24) for applying an electrolytically dressing voltage across the outer-surface grindstone and the outer-surface electrode and across the inner-surface grindstone and the inner-surface electrode, wherein the outer-surface grindstone is dressed electrolytically when the outer-surface grindstone is grinding the end surface and oblique surfaces of the outer periphery of the glass substrate, and during a non-processing period when the glass substrate is being replaced, the inner-surface grindstone is dressed electrolytically.
According to the method and the apparatus of the present invention, as described above, end surfaces and oblique surfaces of outer and inner peripheries of the glass substrate (1) can be ground simultaneously using the outer-surface grindstone (12) and the inner-surface grindstone (14). In addition, during this grinding period, the outer-surface grindstone is dressed electrolytically (also known as xe2x80x9cin-process dressingxe2x80x9d) using the voltage application means (24) while supplying a conductive grinding liquid between the grindstone and the outer-surface surface electrode (18), thereby even when fine grinding particles are used, the outer-surface grindstone can be sharpened, therefore, while maintaining a high efficiency, the workpiece can be processed with a high accuracy and quality. Furthermore, the conductive grinding liquid is supplied between the inner-surface grindstone and the inner-surface electrode (20) when the glass substrate is replaced during a non-work period, the grindstone is dressed electrolytically (also known as xe2x80x9cinterval dressingxe2x80x9d) by the same voltage application means. Therefore, even when similar fine grinding particles are used, the inner-surface grindstone can be sharpened while maintaining high efficiency and can process a workpiece precisely with high quality.
In addition, because the outer-surface grindstone undergoes in-process dressing during grinding, and the inner-surface grindstone undergoes interval dressing during a non-processing period, the load of the voltage application means (24) can be averaged, and compared to an alternate method where both grindstones are dressed at the same time, the power supply facility can be made more compact.
According to a preferred embodiment of the present invention, an electrode (16) for discharge truing is installed in place of the above-mentioned glass substrate (1), the aforementioned outer-surface grindstone (12) and inner-surface grindstone (14) are positioned at a grinding position, the aforementioned electrode (16) and grindstones (12, 14) are charged positive and negative, respectively, and both grindstones are formed by discharge truing.
Using the above method, even if the outer-surface grindstone (12) or inner-surface grindstone (14) deteriorates in terms of shape accuracy after long-term use, an error in the installation of the grindstones caused by removing and remounting the grindstones can be avoided. In addition, the workpiece can be formed with a high accuracy because the grindstones can be subjected to truing by discharge while being mounted. Moreover, the power supply for electrolytic dressing (also referred to as the xe2x80x9cvoltage application meansxe2x80x9d) can be used for discharge truing simply by changing polarity, so the power supply need not have a large supply capacity.
Also, the above-mentioned metal-bonded outer-surface grindstone (12) and metal-bonded inner-surface grindstone (14) have circular cylindrical outer surfaces and frustum-type grooves (12a, 14a) that can contact end surfaces and oblique surfaces of the circular cylindrical surfaces.
In this configuration, edge portions of the glass substrate can be processed precisely with high quality simply by making frustum-type grooves (12a, 14a) of the formed grindstones come into contact with edge portions (also referred to as the xe2x80x9couter peripheryxe2x80x9d and xe2x80x9cinner peripheryxe2x80x9d) of the glass substrate (1).
The aforementioned metal-bonded outer-surface grindstone (12) and/or metal-bonded inner-surface grindstone (14) are provided with a plurality of frustum-type grooves (12a, 14a) with separating intervals around the same axis. With this configuration, if the accuracy of the shape of a groove deviates from the specified value due to wear caused by processing, the grindstone can be shifted axially and the grooves can be used sequentially, thereby the process can be carried out without a stopping, and continuous operation can be greatly extended.
In addition, the above-mentioned metal-bonded outer-surface grindstone (12) and/or metal-bonded inner-surface grindstone (14) are provided with frustum-type grooves (12a, 14a) for rough processing and finish processing, with intervals around the same axis.
Due to this configuration wherein the grindstones are provided with frustum-type grooves for rough processing and finish processing respectively, after the workpiece is processed roughly by rough-processing frustum-type grooves (12a, 14a), the grindstone is shifted in the axial direction, and finish processing frustum-type grooves (12a, 14a) on the same grindstone can be used for finish processing. Therefore, compared to the prior art method in which the worn grindstone is replaced with another fresh grindstone, down-time can be greatly reduced, while avoiding the deterioration of processing accuracy caused by decentering (also known as xe2x80x9caxial deviationxe2x80x9d) of the center of rotation.
Moreover, another preferred embodiment of the present invention is provided with a substrate drive device (32) that drives the glass substrate (1) to rotate around the axial center thereof, an outer-surface grindstone drive device (34) that drives the metal-bonded outer-surface grindstone (12) around the axial center thereof, and an inner-surface grindstone drive device (36) that drives the metal-bonded inner-surface grindstone (14) around the axial center thereof; the substrate drive device, outer-surface grindstone drive device and/or inner-surface grindstone drive device are configured to be movable between the processing position of the glass substrate and a non-processing position where the outer-surface grindstone and the inner-surface grindstone are kept away from the glass substrate while the glass substrate is replaced.
In this configuration, when the metal-bonded outer-surface grindstone (12) and the metal-bonded inner-surface grindstone (14) are positioned at the processing location, the outer-surface grindstone is dressed electrolytically (the process of in-process dressing), while grinding the workpiece, and when both grindstones are positioned at a non-processing location, the glass substrate can be replaced while the inner-surface grindstone is being dressed electrolytically (the process of interval dressing).
The aforementioned substrate drive device (32) is provided with a vacuum suction head (33a) to suck the glass substrate (1) and a supporting head (33b) that supports the glass substrate between the vacuum suction head. This configuration allows the vulnerable glass substrate (1) to be driven and rotated precisely, while being protected when it is sandwiched by the vacuum suction head (33a) and the supporting head (33b).
In another configuration, a detachable discharge truing electrode (16) is sandwiched between the aforementioned vacuum suction head (33a) and the supporting head (33b), and electrode (16) being provided with an outer periphery and inner periphery that match the glass substrate (1). In this configuration, even if the outer-surface grindstone (12) or the inner-surface grindstone (14) deteriorates in terms of shape accuracy after a long-term operation, the grindstone can continue high-accuracy forming by being discharge trued, without the need to remove the grindstone and remount it to the machine, simply by setting the discharge truing electrode (16) in place of the glass substrate (1).
Other objects and advantages of the present invention are revealed according to the following description referring to the attached drawings.